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Nematomorpha
Scientific classification
Domain:	Eukaryota;
Kingdom:	Animalia;
Superphylum:	Ecdysozoa;
Phylum:	Nematomorpha; Vejdovsky, 1886
Classes
	Nectonematoida; Gordioidea

Nematomorpha (sometimes called Gordiacea, and commonly known as Horsehair worms or Gordian worms) are a phylum of parasitic animals that are morphologically and ecologically similar to nematode worms, hence the name. They range in size from 1 cm to 1 meter long, and 1 to 3 millimetres in diameter. Horsehair worms can be discovered in damp areas such as watering troughs, streams, puddles, and cisterns. The adult worms are free living, but the larvae are parasitic on beetles, cockroaches, Orthoptera and crustaceans^[1]. About 326 species are known and a conservative estimate suggests that there may be about 2000 species worldwide.^[2] The name "Gordian" stems from the legendary Gordian knot. This relates to the fact that nematomorpha often tie themselves in knots.^[3]

[edit] Description and biology

Nematomorphs possess an external cuticle without cilia. Internally, they have only longitudinal muscle and a non-functional gut, with no excretory, respiratory or circulatory systems. Reproductively, they are dioecious, with the internal fertilization of eggs that are then laid in gelatinous strings. The larvae that hatch have rings of cuticular hooks and terminal stylets that are believed to be used to enter the hosts. They are mostly free living but males and females aggregate into tight balls (Gordian knots) during mating.^[4]^[5]

Spinochordodes tellinii and its katydid host

In Spinochordodes tellinii, which has orthopterans as its vector, the infection acts on the insect's brain and causes it to seek water and drown itself, thus returning the nematomorph to water.^[4] They are also remarkably able to survive the predation of their host, being able to wriggle out of the predator that has eaten the host.^[6]

[edit] Taxonomy

Nematomorphs can be confused with nematodes, particularly Mermithid worms. Unlike Nematomorphs, Mermithids do not have a terminal cloaca. Male mermithids have one or two spicules just before the end apart from having a thinner, smoother cuticle, without areoles and a paler brown colour.^[7]

The phylum is placed along with the Ecdysozoa clade of moulting organisms that include the Arthropoda. Fossilized worms have been reported from Early Cretaceous Burmese amber dated to 100–110 million years apart from a fossil from the Mesozoic.^[8]

Relationships within the phylum are still somewhat unclear, but two classes are recognised:

Class Nectonematoida: Marine, planktonic, with a double row of natotory setae along each side of the body; with dorsal and ventral longitudinal epidermal cords, blastocoelom spacious and fluid filled; gonads single; larvae parasitise decapod crustaceans
Class Gordioidea: Freshwater and semiterrestrial; lack lateral rows of setae; with a single, ventral epidermal cord; blastocoelom filled with mesenchyme in young animals but becomes spacious in older individuals; larvae primarily parasitise Orthoptera

[edit] References

^ Hanelt, B, F. Thomas, and A. Schmidt-Rhaesa (2005). "Biology of the phylum Nematomorpha". Advances in Parasitology 59: 244–305. doi:10.1016/S0065-308X(05)59004-3.
^ Poinar Jr., G (2008). "Global diversity of hairworms (Nematomorpha: Gordiaceae) in freshwater". Hydrobiologia 595 (1): 79–83. doi:10.1007/s10750-007-9112-3.
^ Piper, Ross (2007), Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals, Greenwood Press.
^ ^a ^b Thomas, F.; Schmidt-Rhaesa, A., Martin, G., Manu, C., Durand, P., and Renaud, F. (May 2002). "Do hairworms (Nematomorpha) manipulate the water seeking behaviour of their terrestrial hosts?". J. Evol. Biol. 15 (3): 356–361. doi:10.1046/j.1420-9101.2002.00410.x. ISSN 1010-061X. http://www.erin.utoronto.ca/~w3gwynne/BIO418/Nemato.pdf. — according to Thomas et al., the "infected insects may first display an erratic behaviour which brings them sooner or later close to a stream and then a behavioural change that makes them enter the water", rather than seeking out water over long distances.
^ Schmidt-Rhaesa, Andreas (2002). "Two Dimensions of Biodiversity Research Exemplified by Nematomorpha and Gastrotricha". Integrative and Comparative Biology 42 (3): 633–640. doi:10.1093/icb/42.3.633.
^ Ponton, Fleur; Camille Lebarbenchon, Thierry Lefèvre, David G. Biron, David Duneau, David P. Hughes, and Frédéric Thomas (April 2006). "Parasitology: Parasite survives predation on its host". Nature 440 (7085): 756. doi:10.1038/440756a.
^ Malcolm S. Bryant, Robert D. Adlard & Lester R.G. Cannon 2006. Gordian Worms: Factsheet. Queensland Museum. [1]
^ Poinar, George; Buckley Ron (2006) Nematode (Nematoda: Mermithidae) and hairworm (Nematomorpha: Chordodidae) parasites in Early Cretaceous amber. Journal of invertebrate pathology 93(1):36–41

[edit] Further reading

Baker GL, Capinera JL (1997). "Nematodes and nematomorphs as control agents of grasshoppers and locusts". Memoirs of the Entomological Society of Canada 171: 157–211.
Poinar GO Jr (1991). "Nematoda and Nematomorpha". in Thorp JH, Covich AP. Ecology and Classification of North American Freshwater Invertebrates. San Diego, CA: Academic Press. p. 249–283.
Thorne G (1940). "The hairworm, Gordius robustus Leidy, as a parasite of the Mormon cricket, Anabrus simplex Haldeman". Journal of the Washington Academy of Science 30: 219–231.

[edit] External links

Nematomorpha Biodiversity Project website. Provides pictures, life cycle information and searchable databases.
horsehair worms on the UF / IFAS Featured Creatures Web site

[edit] Videos

Videos of a cricket infected with a Gordian worm with the worm emerging to mate, as well as emerging from predators that have eaten the infected cricket. From Nature, April 2006.
Nematomorph worm at YouTube (requires Adobe Flash) — explains the proteome research done on this worm
The cricket suicide (video)

[0] Hanelt, B, F. Thomas, and A. Schmidt-Rhaesa (2005). "Biology of the phylum Nematomorpha". Advances in Parasitology 59: 244–305. doi:10.1016/S0065-308X(05)59004-3.

[1] Poinar Jr., G (2008). "Global diversity of hairworms (Nematomorpha: Gordiaceae) in freshwater". Hydrobiologia 595 (1): 79–83. doi:10.1007/s10750-007-9112-3.

[2] Piper, Ross (2007), Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals, Greenwood Press.

[manipulate-3] Thomas, F.; Schmidt-Rhaesa, A., Martin, G., Manu, C., Durand, P., and Renaud, F. (May 2002). "Do hairworms (Nematomorpha) manipulate the water seeking behaviour of their terrestrial hosts?". J. Evol. Biol. 15 (3): 356–361. doi:10.1046/j.1420-9101.2002.00410.x. ISSN 1010-061X. http://www.erin.utoronto.ca/~w3gwynne/BIO418/Nemato.pdf. — according to Thomas et al., the "infected insects may first display an erratic behaviour which brings them sooner or later close to a stream and then a behavioural change that makes them enter the water", rather than seeking out water over long distances.

[4] Schmidt-Rhaesa, Andreas (2002). "Two Dimensions of Biodiversity Research Exemplified by Nematomorpha and Gastrotricha". Integrative and Comparative Biology 42 (3): 633–640. doi:10.1093/icb/42.3.633.

[5] Ponton, Fleur; Camille Lebarbenchon, Thierry Lefèvre, David G. Biron, David Duneau, David P. Hughes, and Frédéric Thomas (April 2006). "Parasitology: Parasite survives predation on its host". Nature 440 (7085): 756. doi:10.1038/440756a.

[6] Malcolm S. Bryant, Robert D. Adlard & Lester R.G. Cannon 2006. Gordian Worms: Factsheet. Queensland Museum. [1]

[7] Poinar, George; Buckley Ron (2006) Nematode (Nematoda: Mermithidae) and hairworm (Nematomorpha: Chordodidae) parasites in Early Cretaceous amber. Journal of invertebrate pathology 93(1):36–41

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